In die packaging, a die's pads are attached to connectors or other leads which in turn, are connected to other circuitry. FIG. 1 shows a die lead 11 which has a die pad 12 (or bump) on its top surface. Die pads are at the outer perimeter or edges of a die and act as the die's output terminals.
In packaging the die, the die's pads are typically attached to connectors which are commonly referred to as tape leads 13 which are a group of leads formed into an array of side-by-side leads. During bonding, the die pad 12 is used as the welding material.
After a die pad 11 is connected to a tape lead 13, the lead tape is, in turn, connected to other circuitry such as a bond finger on a package (not shown). The connection of the die pads to the tape leads is often referred to as "inner-lead bonding," and the connection of the tape leads to, for example, a package or leadframe is referred to as the "outer-lead bonding."
To perform inner-lead bonding or outer-lead bonding, either of two techniques can be used. First, gang bonding, which uses thermal compression, can be used to make all connections simultaneously. Alternatively, a more precise bonding method includes the use of a single point bonding tool to make each connection individually. A single point bonding tool uses force, heat and ultrasonic vibration to weld the leads together. As shown in FIG. 1, to make the connection, the leads are positioned so that one is on top of the other. The single point bonding tool then makes contact with the lead on top, applying force, heat and ultrasonic vibration thereto. The die pad welds the leads together to make the connection.
Even with the improved accuracy of the single point bonding method, when using the single point bonding tool of the prior art, there is a tendency for the connected leads to be misaligned. Referring to FIG. 2, a single point bonding tools of the prior art has at its tip 14, a depressed cross hatching similar to a female phillips screw driver. The depressed portion is indicated by cross area 16 and the surface of the tip's distal end is indicated by shaded area 17. When using this prior art tool, if the leads prior to bonding are not in alignment when the surface of the tool makes contact with the top lead, there is no mechanism by which to correct the misalignment. The bonding tool simply presses down on the top lead and the bonding takes place.
In some cases, there are over three hundred lead connections to make per package. Therefore, if misalignment occurs and an inadequate connection is made which either results in a weak connection or a short, the loss in manufacturing time and materials is substantial. Misalignment can be caused by shrinkage factors, bent leads and also tolerances in other assembly steps.